Ken,

IMO I would avoid feeding that much tuna. A tidbit every now and then
is ok, but that amount could cause long-term health problems.

Can she tolerate those "hairball treats?" Lots of cats like them. You
feed 3-5 pieces or so per day.

I am surprised that Metamucil (psylium fiber) does not work, since
it's designed to bulk up the stool similar to the pumpkin. How long
did you try this?

Will she eat any other kind of squash, such as (plain) acorn or
butternut? Pumpkin is in the squash family so these should work also.

I don't know of any other treatment, except for regular brushing and
Petrolmalt.

Rene